System for displaying the subscription state of a pay broadcasting program

A system for displaying the subscription state of a pay broadcasting program, comprising:

• an encoder, comprising:
• (a) program signal scrambling means for scrambling a pay program signal using a random number so as to produce a scrambled pay program signal,
• (b) random number generating means for generating the random mumber,
• (c) means for determining an initial value for said random number generating means,
• (d) key data generating means for generating key data obtained by coding, using a subscriber's first coding data, subscribed program data showing a kind of pay subscription program to be offered to the subscriber, and
• (e) a transmitter for transmitting a broadcasting signal containing said key data as secret data, a subscriber's second coding data identifying the subscriber, current program data representing the pay program currently being broadcast, and said scrambled pay program signal;
• and
• a decoder for decoding said broadcasting signal for display, comprising:
• (a) a common data detector for extracting said current program data,
• (b) an individual data detector for extracting said key data as said secret data and for extracting said second coding data,
• (c) a first comparator for detecting a coincidence between said second coding data extracted by said individual data detector and coding data which is used to identify said decoder,
• (d) a first control circuit enabling said key data which has been extracted by said individual data detector to be stored in a memory in response to a coincidence output of said first comparator,
• (e) signal generating means for generating a subscriber program request signal when the subscriber wishes to view a subscribed pay program,
• (f) controlling means for detecting said subscribed program data from said key data and for writing said subscribed program data into said memory only when said key data has been enabled to be written into said memory,
• (g) a second comparator for comparing said subscribed program data written by said controlling means into said memory with said current program data extracted by said common data detector,
• (h) a subscribed program data decoder for decoding said subscribed program data from said key data stored in said memory using the subscriber's first coding data,
• (i) a second control circuit for controlling said subscribed program data decoder in response to a coincidence signal from said second comparator,
• (j) random number generating means having an initial value set using said subscribed program data decoded from said key data by said subscribed program data decoder for generating a random number for descrambling said scrambled pay program signal,
• (k) descrambling means for descrambling said scrambled pay program signal with the use of said random number from said random number generating means, and
• (l) alarm means for producing an alarm when said second control circuit is not enabled in response to the comparison output of said second comparator.